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I've got a mechanical fuel pump. Twice lately I've tried to start the car and I can't get it to fire. It turns over fine. One of those two times it eventually fired and ran ok. The other time I just gave up. Yesterday it fired up on start but then felt like it was starving for fuel for most of the trip. I stopped at the grocery store and when I left it fired up but barely ran. Eventually it cleared up and ran OK. The reason I think it's the fuel pump is I don't smell gas at all when it's not firing. I looked down the carb and I wasn't getting a shot of fuel when I pumped it.
Will a mechanical fuel pump run intermittently when it's starting to go? It's about 12 years old and probably has less than 20k on it.
To compound the diagnosis I recently replaced the carb so that could be the problem..... It's a q-jet rebuilt by a pretty well known guy in the business so I don't think that's the problem. I suppose it could be water in the fuel, I run 93 octane with ethanol (it won't run worth a crap on 91 non-ethanol which is all I can get around here).
I haven't even pulled the fuel filter to dump it out to see if there's any water yet....
Mike disconnect the fuel line IN to your carburetor and route it into an empty coffee can. Crank the engine and you should get positive flow from the fuel pump. If not you know that the pump is on the way out or you could have a problem with your fuel sending unit. Have you ever dropped the tank and installed new hose between the tank and fuel lines? If the hose gets old and dry rotted the pump won't be able to get fuel from the tank easily.
Mike disconnect the fuel line IN to your carburetor and route it into an empty coffee can. Crank the engine and you should get positive flow from the fuel pump. If not you know that the pump is on the way out or you could have a problem with your fuel sending unit. Have you ever dropped the tank and installed new hose between the tank and fuel lines? If the hose gets old and dry rotted the pump won't be able to get fuel from the tank easily.
Everything was brand new when I built the car in the late 2000's I have stainless supply and return lines. The only rubber lines are at the top of the tank to the rearward stainless lines and from the forward end of the stainless lines to the fuel pump (which is where my fuel filter is). All the rubber lines were new then
I'm definitely getting gas or it wouldn't start at all. It just seems intermittent.
A vacuum gauge doubles as a fuel pressure gauge, hook it up to your fuel line from the pump and you should see 6-7 pounds of pressure.
Thank you. That's a good idea. I have a fuel pressure tester... The only problem is I'm hard-lined (correctly) from the fuel pump to the carb. I can probably half-*** something to T it in and test it though.
Last edited by allyolds68; July 29th, 2019 at 11:29 AM.
Is there a chance you inserted the fuel filter incorrectly - oriented in the opposite direction relative to the check-valve being backwards and/or you either forgot the fuel filter spring or inserted the spring in the incorrect orientation? It could be that simple. You'll certainly find out when you unhook the fuel inlet line from the carburetor. Check the orientation of the fuel filter and ensure the spring is inserted correctly.
When I had the carb rebuilt on my 69 Cutlass the rebuilder gave me some strict instructions. He found the previous owner used a filter with a check valve in it. The rebuilder said that was the wrong filter. I checked my Chilton manuals and if my memory serves me right, they said the check valve filter did not come out until 1976. He also told me do not even use the check valve filters even in the newer engines. His explanation was the ethanol in the newer gas will swell the check valve blocking fuel flow and leaving you stranded on the side of the road. Even with some of the newer ethanol compatible parts I still heed his warning just in case I would get some older filters that were not compatible.
It was a the original Rochester Quadra jet 4 bbl. with a divorced choke. Some one had put the newer check valve filter in it. The rebuilder removed it and put a non check valve filter back in it on the rebuild. If my memory serves me right there was another thread on here talking about some of the other rebuilders not using them also because the restrict fuel flow for racing applications.
It would appear to me, based upon the image contained w/in the 1971 CSM for the Rochester Quadrajet Model 4MC, the check-valve orientation is depicted on the left-hand side of the fuel filter image. Again, it appears that way to me. This is the orientation of the fuel filter I employ w/ the check valve. Regardless if there is or there is not a check-valve in this image, the correct orientation of the spring and fuel filter remains the same as depicted in the image.
While you are in there with the fuel line disconnected, make a gravity feed fuel bottle and run the carb off it for a bit to see if your problems go away.
I checked my Chilton manuals and if my memory serves me right, they said the check valve filter did not come out until 1976. He also told me do not even use the check valve filters even in the newer engines.
That sounds about right. I worked at auto parts stores through high school and college and the catalogs showed check valves in the later listings but not in the earlier ones.
I also agree about not using a check valve type filter in a high performance application. I heard many folks relay issues with higher RPM fuel delivery when using the check valve type filters.
That sounds about right. I worked at auto parts stores through high school and college and the catalogs showed check valves in the later listings but not in the earlier ones.
I also agree about not using a check valve type filter in a high performance application. I heard many folks relay issues with higher RPM fuel delivery when using the check valve type filters.
I would argue, if you're truly in a high performance application (turning a 1/4 mile every weekend at the strip) - I would use no fuel filter - period.
I actually bought a new fuel pump that was bad. Car would run fine for a while, then with no warning while sitting idling it would die. The only way it would start was by pouring gas into carb bowl. After that it would run fine until it decided to take a dump again. I changed the fuel pump and have had no issues since.
I would argue, if you're truly in a high performance application (turning a 1/4 mile every weekend at the strip) - I would use no fuel filter - period.
Restricting fuel to the carb also affects street performance, not just drag only vehicles. Lotsa folks have performance daily drivers that aren't track only cars.
Last edited by Fun71; July 30th, 2019 at 07:28 PM.
I've had no time to work on it so I lazily threw a $25 Airtex fuel pump in it last night and it fired right up. Drove it to work today without any issues...
I've had no time to work on it so I lazily threw a $25 Airtex fuel pump in it last night and it fired right up. Drove it to work today without any issues...
So, I know this thread is a couple of years old, but it was up the alley that I'm working. I have a 1972 Cutlass with a 455 4bbl. For a while it would shutter while normal driving, especially at high throttle. Didn't think to much of it. Then it stalled out a couple of times, but I was able to restart it. Then it died. I surmised that it was a fuel issue. The car had a new after market fuel pump, and the in line filter looked clean. Someone mentioned that it sounded like sediment in the fuel tank that was clogging up the lines. So, I dropped the tank. The filer bag around the Fuel Sending Unit had disintegrated. I replaced the FSU, tank, tank straps, cleaned out the fuel lines, and removed the in line filter and went with the filter at the base of the carb. Still didn't start. When I checked the fuel pump, (holding thumb over the 3/8" fuel in line, I did not feel vacume. Bought a new fuel pump.
Here's the question: When installing the fuel pump, mechanical, how can you ensure that the lever is resting on top of the cam? I don't want to mess this up, because I believe that it can make life interesting if that is not installed correctly.
So, I know this thread is a couple of years old, but it was up the alley that I'm working. I have a 1972 Cutlass with a 455 4bbl. For a while it would shutter while normal driving, especially at high throttle. Didn't think to much of it. Then it stalled out a couple of times, but I was able to restart it. Then it died. I surmised that it was a fuel issue. The car had a new after market fuel pump, and the in line filter looked clean. Someone mentioned that it sounded like sediment in the fuel tank that was clogging up the lines. So, I dropped the tank. The filer bag around the Fuel Sending Unit had disintegrated. I replaced the FSU, tank, tank straps, cleaned out the fuel lines, and removed the in line filter and went with the filter at the base of the carb. Still didn't start. When I checked the fuel pump, (holding thumb over the 3/8" fuel in line, I did not feel vacume. Bought a new fuel pump.
Here's the question: When installing the fuel pump, mechanical, how can you ensure that the lever is resting on top of the cam? I don't want to mess this up, because I believe that it can make life interesting if that is not installed correctly.
Thanks all
Pete
You won't mess it up. The curvature of the arm and bolting it in flush will ensure that it is in hte correct position. If becomes very difficult to push the pump in, rotate the engine to get the cam lobe in a different position and it should slide in easier.
You won't mess it up. The curvature of the arm and bolting it in flush will ensure that it is in hte correct position. If becomes very difficult to push the pump in, rotate the engine to get the cam lobe in a different position and it should slide in easier.
July 29th, 2019, 09:31 AM
